Gordon Brown has decided to take a tougher line against "vested interest" occupations he believes are blocking public sector reform, including doctors, police, bankers and post office workers, cabinet sources say.

Ministers are studying fresh ways to highlight their resolve to make society more responsible, a big theme of the prime minister's recent speech to Labour's conference. They include legislation against bankers, "powers of recall" for inefficient police, and a requirement that patients be offered private sector help if local primary care or hospital services are inadequate.

Brown, the cabinet sources say, decided in the past few weeks to adopt a tougher pro-public sector reform stance, in order that his defence of the state in the face of recent attacks on big government by David Cameron does not become confused with complacency about the current performance of the public sector.

Ministers are also determined to back up Royal Mail's management by warning the postal workers' union, especially in central London, that it is destroying the principle of a universal postal service by going ahead with planned strikes.

Ministers are determined not to be neutral between the unions and management, even if it causes tensions with some Labour MPs.

Being more explicit about some of the unaccountable forces holding Britain back, Downing Street believes, would give Brown greater definition in the run-up to an election. Part of the task will be for him to adopt a tougher rhetorical line than he has so far.

Number 10 remains convinced that the election must be a "big choice" election, rather than a contest between two centrist characters.

The tougher stance requires ministers to restate the pro-consumer themes laid out in the Building Britain's Future, the government's main pre-election manifesto document. That document proposed that consumers be given some form of legal right of redress, including access to alternative providers, if the public sector does not provide an adequate service.

Ministers are also exploring tax raising measures on the rich in a pre-budget report that the Conservatives would have difficulty endorsing.

Labour hopes to portray the Tories as not just anti-public sector reform, but ideologically opposed to the state.

In a sign of the attack likely to be mounted on Cameron by Labour in the coming months, the business secretary and effective deputy prime minister, Lord Mandelson, today accused the Tory leader of a "pathological aversion to reality by blaming the government for the credit crunch".

Attacking Cameron's controversial conference speech blaming big government for Britain's ills, Mandelson said: "I don't think I oversimplify when I say that the core of his argument ran like this: the problem, essentially, is government. Too much of it. The government is a check on enterprise, a check on growth. It is standing in the way. So let's get rid of it, or at least cut it down to size."

Speaking at a conference in Oxford, Mandelson said: "If you start with an ideological assumption that government is the problem, you will inevitably think the issue is big versus small government. And you will inevitably base your prospectus for government on how to cut it, regardless of the consequences"

He added: "To argue for cuts and have nothing to say about growth reveals a dogmatic mind, rather than a pragmatic one. It is to ignore the simple fact that the fastest way to get the country out of debt is to get the country out of the recession."

But Mandeslon tempered his defence of the state by describing statism – a belief in standardised mass-produced public services and the centralising instinct that says the man in Whitehall knows best – as an obstacle to thinking about the necessary role of government in a modern economy.

But he admitted: "We all recognise that the next few years will be defined by the need to return the public finances to a sustainable balance. We need to renew the public sector reform agenda as a way of pushing up public sector productivity and return on investment".

Reform, he argued, is essential, since "it will be necessary to constrain and cut lower priority public spending while protecting front line services".